The present invention relates generally to an intensifier piston capable of multiple intensification rates.
Intensifier pistons can be used in a variety of applications in which it is necessary to intensify the pressure of a fluid from a first pressure to a second pressure. For example, intensifier pistons are very common in valve actuators and fuel injectors. Specifically, in a fuel injector, the intensifier is used to increase the fuel pressure from low or medium pressure to high pressure for fuel injection.
Intensifier pistons in a fuel injector can be cam operated or hydraulically operated. With a hydraulically operated intensifier, the top of the intensifier piston is exposed to a pressurized fluid causing the piston to move downward, thereby moving a plunger and pressurizing low pressure fuel in a pressurization chamber. The rate of intensification depends upon the pressure of the actuation fluid on top of the intensifier piston as well as the area of the intensifier piston exposed to the actuation fluid.
When intensifiers were first used in fuel injection systems, they were only able to provide one rate of intensification per injection event. This initial problem was solved with a development of a stepped top piston as illustrated in U.S. Pat. No. 5,826,562 issued Chen et al. The stepped top piston allows two different intensification rates during a single injection event. Actuation fluid is exposed to a first area, on the stepped top, causing a first intensification rate. As the piston moves downward, the stepped top comes out of its bore exposing a second actuation area, the shoulder of the intensifier, to actuation fluid and increasing the intensification ratio. Although this is a beneficial design, improvements can be made. First, there is no ability to choose intensification rates; every injection event gets both intensification profiles. Second, the design is inefficient with its actuation fluid usage because the second area must be filled with fluid as the piston moves down before the second area becomes effective. This results in the need for extra actuation fluid in the cavity, a slight delay in increased pressurization and difficulty in fully returning the plunger between injections, especially in cold conditions.
The present invention is designed at overcoming one or more of the above problems.
In the first embodiment of the present invention, a fuel injector comprises a barrel defining a first fluid passage, a second fluid passage, and a piston bore with an upper bore and a lower bore. An intensifier piston includes a shoulder and a stepped top. A first actuation cavity is defined by the upper bore, the stepped top and the first fluid passage and a second actuation cavity is defined by the lower bore, the shoulder and the second fluid passage. The piston is slidably received in the piston bore, wherein the shoulder is received in the lower bore and the stepped top is received in the upper bore. The stepped top has a first surface open to fluid pressure in the first actuation cavity and the shoulder has a second surface open to the fluid pressure in the second actuation cavity. The piston is movable between the first position and the second piston and the stepped top is sealable with the upper bore when the piston moves between the first position and the second position. Additionally, the fuel injector comprises a source of actuation fluid, a drain passage, and a control valve to open and close fluid communication between the first and second fluid passages and the source of actuation fluid and the drain.
In a second embodiment of the present invention, a method for operating an intensifier piston, having a first effective area and a second effective area, comprises delivering a first fluid flow from a common fluid source to the first area, moving the intensifier piston a first pre-selected distance, delivering a second fluid flow from the common fluid source to the second area, moving the intensifier piston a second pre-selected distance, and maintaining the first area in direct fluid isolation from the second area.
In the third embodiment of the present invention, a method for operating an intensifier piston system includes delivering a first signal, moving a valve to a first position response to the first signal, allowing fluid flow to a first effective area of an intensifier piston, delivering a second signal, moving the valve to a second position response to the second signal and allowing the fluid flow to a second effective area of the intensifier piston.
In a fourth embodiment of the present invention, an intensifier assembly comprises a barrel defining a first fluid passage, a second fluid passage and a piston bore having an upper bore and a lower bore. An intensifier piston includes a shoulder and a stepped top. A first actuation cavity is defined by the upper bore, the stepped top and the first fluid passage. A second actuation cavity is defined by the lower bore, shoulder and the second fluid passage. The piston is slidably received in the piston bore, wherein the shoulder is received in the lower bore and the stepped top is received in the upper bore. The stepped top has a first surface open to fluid pressure in the first actuation cavity and a shoulder has a second surface open to fluid pressure in the second actuation cavity. Finally, the piston is movably between a first position and a second position wherein the stepped top is sealable with the upper bore when the piston moves between the first position and the second position.